Rc 612

Prior to the analysis, soil samples were sieved (2 mm mesh) and dried at 105 °C. The content of sand, silt and clay was determined by a combination of sieving and sedimentation, and the soil pH was tested with a pH-meter after extraction with water in a 1:5 (w:v) ratio. Organic carbon was assessed using the dry combustion technique with a Leco RC-612. Total sulfur was measured with a Leco SC-144 DR. Total nitrogen was determined using the Kjeldahl method. The soil was digested in H₂SO₄ with Kjeltabs (K₂SO₄ + CuSO₄·5H₂O; Foss Tecator Digestor Auto) followed by distillation in a Foss Tecator Kjeltec 2300 Analyser Unit. To determine the concentration of pseudo-total (hereafter referred to as “total”) and EDTA metals, two soil extraction methods were applied: hot concentrated HClO₄ (Foss Tecator Digestor Auto; Ca, Cd, K, Mg, Pb, Tl, Zn) and 0.05 M EDTA (Cd, Pb, Tl, Zn). The metal concentrations in soil extracts were analyzed by flame atomic absorption spectrometry (Varian 220 FS). The total phosphorus was measured using the molybdenum blue method with a colorimeter (Hach-Lange DR 3800) after digestion in hot HClO₄. Available (Olsen) phosphorus was measured with an ion chromatograph (Dionex ICS-1100) following the extraction of soil with 0.5 M NaHCO₃, pH 8.5.

Detailed petrographic analyses were conducted on thin sections of all samples using a Zeiss SteREO Discovery.V8 stereo microscope linked to an AxioCam MRc5 5-megapixel camera. A subset of well-preserved samples that contained organic matter was subsequently analysed by all other methods.
Total organic carbon (TOC) contents were determined with a Leco RC612 multiphase carbon/hydrogen analyser, where carbon was measured as CO₂ with an infrared detector. Prior to analysis, barite was finely ground (≤50 µm) in a swing mill (MM 400, Retsch GmbH, Haan, Germany). A significant contribution of CO₂ from fluid inclusions to the TOC value is unlikely because most volatiles were released during grinding.